A method of this type is known from DE 10 2007 062 820 A1. Another method of the type recited supra is for example implemented by the control software LMaster of Loesche GmbH, Duesseldorf.
A vertical mill that is controllable by a method of this type is disclosed for example by DE 1 507 579 B. Vertical mills of this type are used in particular in the concrete industry and in coal power plants for grinding brittle material to be ground or grinding material, for example raw meal (as a pre product for concrete production) cement clinker, limestone in general, coal, clay, gypsum or slag sand.
A vertical mill is essentially made form one or plural mills with a rotating grinding plate as a common grinding element and a respective rolling element rolling on the grinding element. The rolling elements can be geometrically configured as spheres or cylindrical, conical or convex rollers. The wearing surfaces of the grinding element and of the rolling element can be provided with highly wear resistant jackets, for example made from chilled cast iron.
During operations of vertical mills the material to be ground is typically applied from above to a center of the grinding element, moves from there under its own weight and through centrifugal forces in a radial outward direction and is ground by the rollers. Thus a layer of partially ground grinding material with different grit sizes is formed on the grinding element. This layer is designated as grinding bed and continuously moves towards the edge of the grinding element and beyond. Depending on grinding material and application water is additionally applied to the grinding element.
At an edge of the grinding element particles of the grinding material fall into a ground material bowl of the vertical mill which ground material bowl is arranged under the grinding element. Depending on the application the particles from the ground material bowl are sifted according to grit sizes, wherein particularly coarse particles are provided to the grinding element again. Quite frequently dust shaped particles are carried out of the grinding bed in upward direction by a vertically rising air flow into a sifter arranged above the grinding element.
A mechanical condition of the grinding bed during rollover, its stability and grinding bed elevation on the grinding element essentially define an effectivity of the grinding process. The known method monitors the grinding bed elevation and fineness and volume of the carried out particles and automatically adapts control variables of the vertical mill when the measured parameters deviate from a defined nominal condition of the vertical mill.
The typical control variables of a vertical mill, the grinding material flow and depending on the application an adjustable grinding pressure on the rollers, a volume of water applied to the grinding element or a volume of the air flow and a sifter speed of rotation are only linked very indirectly and to a large extent in a nonlinear manner with the measured control variables of fineness and volume of the carried out particles. A correct adaptation of the control variables is therefore very complex and error prone.
DE 10 2007 062 820 A1 recited supra proposes for grinding coal to control a grinding bed level with fuzzy rules that are not defined in more detail so that a “rattling” of the mill is prevented. For measurement and control variables sifter air flow, -temperature, -sifted grit size and sifter speed of revolution, grinding material mass flow (the so called “mill load”) grinding pressure, grinding bed height, grinding material grinding properties (e.g. Hardgrove number) and storage volume and NOx-emission or a flame image of a burner connected downstream of the mill and a pressure difference between mill inlet and mill outlet of the hot drying air flowing through the mill including the pulled along dried carbon dust particles and the water that is evaporated from the carbon are suggested.